This invention relates to an apparatus which is capable of correcting an object image displacement.
Recently, there have been proposed various optical apparatus such as cameras and binoculars capable of correcting an image displacement, particulary resulting from a shake of the apparatus relative to an object. In such optical apparatus, various sensors are used such as an acceleration speed sensor, an angular velocity sensor, and an area sensor comprising a multitude of photoelectric conversion elements or Charge Coupled Device (CCD) arrayed in a two-dimensional form. With use of the above sensor, a displaced amount (or shake amount) of an object image due to a shake of the apparatus is detected, and a displacement of the object image is corrected in such a manner as to cancel the shake amount. Also, video cameras and electronic still cameras having a function of correcting an object image displacement similar to the above are available on the market.
A known camera having the above correcting function is such that a displacement of an object light image is corrected by detecting a shake amount at a predetermined time interval, calculating an estimative shake amount based on the detected shake amount to set the estimative shake amount as target position data, and outputting the target position data to a lens drive unit to drive a correction lens to the target position.
One example of the shake correction executed by a conventional camera is described with reference to a timing chart of FIG. 17. FIG. 17 shows a state of an actual shake (shown by the curve M) and a follow-up movement of a correction lens that is driven by a lens drive unit to follow up the actual shake amount (shown by the bold zigzag line) wherein the horizontal coordinate denotes time, the vertical coordinate denotes a shake amount, and T denotes a time interval (or referred to as a "shake detection period") at which the shake amount is detected. An estimative shake amount that is assumed to be obtained at a lapse of each time T is outputted to the driving unit as target position data at respective timings shown by the upward arrow .uparw. to start a shake correction at the respective timings. More specifically, when the target position data is set in the lens drive unit, a drive motor of the lens drive unit having a certain driving performance, drives the correction lens toward the target position. The correction lens is so constructed as to reach the target position at least by the lapse of each time T, considering the driving performance of the motor. After reaching the target position, the correction lens is set in a stand-by state at the target position until the lapse of the time T. Thus, the follow-up movement of the correction lens to cancel the shake amount is repeated cyclically at the lapse of each time T.
In the above shake correction, a displacement of an object light image is detected by the area sensor, the detected displacement is written in a memory as data about image displacement, a shake amount is calculated based on the data, and an estimative shake amount is calculated based on the shake amount. Thereafter, the correction lens is driven based on the estimative shake amount data inputted to the lens drive unit. Accordingly, a certain time is required until start of driving the correction lens. In other words, since the driving of the correction lens is executed at a certain time interval, a time lag is generated between the follow-up movement of the correction lens and the shake detection, and accordingly, the performance of the correction lens is restricted. Further, the correction lens is set in a stand-by state for a certain period at the target position because the correction lens already reaches the target position by the lapse of each time T. Accordingly, what is obtained as the follow-up movement of the correction lens is a stepped configuration as shown by the bold line in FIG. 17, far from the smooth curved shape M representing the actual shake amount.